The molecular structure of basement membranes will be studied by analyzing the main constituents of the basement membrane from human placental tissue. The collagenous and noncollagenous proteins will be isolated after limited proteolysis and characterized by determination of their molecular weight, amino acid composition and by partial amino acid sequence analysis. Antibodies will be produced and used as a tool in the structural studies. Electron microscopy will be done on intact basement membranes and on isolated basement membrane collagens. Electron microscopy and X-ray diffraction will be done on intact basement membranes to search for periodic structures.